SQS FIFO + SWF

• SQS FIFO (First-In-First-Out) Queues have all the capabilities of the standard queue with additional capabilities designed to enhance messaging between applications when the order of operations and events is critical, or where duplicates can't be tolerated.

• SWF provides useful guarantees around task assignments. It ensures that a task is never duplicated and is assigned only once. Thus, even though you may have multiple workers for a particular activity type (or a number of instances of a decider), SWF will give a specific task to only one worker (or one decider instance).

• Additionally, SWF keeps at most one decision task outstanding at a time for a workflow execution. Thus, you can run multiple decider instances without worrying about two instances operating on the same execution simultaneously. These facilities enable you to coordinate your workflow without worrying about duplicate, lost, or conflicting tasks.